Ink drops with touch input are redundant on Windows since the OS does something similar

ui/views/animation/ink_drop_host_view.cc

Index: ui/views/animation/ink_drop_host_view.cc
diff --git a/ui/views/animation/ink_drop_host_view.cc b/ui/views/animation/ink_drop_host_view.cc
index e6b1e424155d41e75056cdf1744fc2e7e2684fcc..5f9ae23bb12e1956b2b880f109e7015dd01176ad 100644
--- a/ui/views/animation/ink_drop_host_view.cc
+++ b/ui/views/animation/ink_drop_host_view.cc
@@ -172,6 +172,37 @@ gfx::Point InkDropHostView::GetInkDropCenterBasedOnLastEvent() const {
 
 void InkDropHostView::AnimateInkDrop(InkDropState state,
                                      const ui::LocatedEvent* event) {
+#if defined(OS_WIN)
+  // The reason for this code is to ensure the ink-drop never gets "stuck"

[Evan Stade, 2016/06/27 15:19:46]

I think you're skipping ahead a bit here, imo the right lead would be "Don't
initiate ink drops for touch events on Windows." Also I'd much prefer if you
didn't copy the code into the comments but integrated the code and comments
instead. How about this:

// Don't create new ink drops for touch events on Windows. However, touch events
must dismiss existing ink drop animations.
if (event && event->IsGestureEvent()) {
  // The ink-drop should never transition to a "pending" state from a touch
  // event.
  if (state == InkDropState::ACTION_PENDING || state ==
InkDropState::ALTERNATE_ACTION_PENDING)
    return;

  // If the state is already "pending", presumably from a non-touch event such
  // as mouse or keyboard, then a triggered action state should be allowed.
Conversely if the state is already targeted to hidden then the touch should be
ignored.
  if ((state == InkDropState::ACTION_TRIGGERED ||
      state == InkDropState::ALTERNATE_ACTION_TRIGGERED) &&
      ink_drop_->GetTargetInkDropState() == InkDropState::HIDDEN)
    return;
}

+  // because of mismatched events or states.
+  //
+  // The ink-drop should never transition to a "pending" state from a touch
+  // event. This is the first part of the conditional:
+  //
+  // state == InkDropState::ACTION_PENDING ||
+  // state == InkDropState::ALTERNATE_ACTION_PENDING
+  //
+  // If the state is already "pending", presumably, from a non-touch event such
+  // as mouse or keyboard, then a triggered action state should be allowed. The
+  // second part of the conditional:
+  //
+  // (state == InkDropState::ACTION_TRIGGERED ||
+  //  state == InkDropState::ALTERNATE_ACTION_TRIGGERED) &&
+  // ink_drop_->GetTargetInkDropState() == InkDropState::HIDDEN
+  //
+  // Finally, all of the above is predicated on the event itself being a
+  // gesture/touch event:
+  //
+  // event && event->IsGestureEvent()
+  //
+  if ((state == InkDropState::ACTION_PENDING ||
+       state == InkDropState::ALTERNATE_ACTION_PENDING ||
+       ((state == InkDropState::ACTION_TRIGGERED ||
+         state == InkDropState::ALTERNATE_ACTION_TRIGGERED) &&
+        ink_drop_->GetTargetInkDropState() == InkDropState::HIDDEN)) &&
+      event && event->IsGestureEvent())
+    return;
+#endif
   last_ripple_triggering_event_.reset(
       event ? ui::Event::Clone(*event).release()->AsLocatedEvent() : nullptr);
   ink_drop_->AnimateToState(state);